A pneumatic circuit for supplying compressed air from an air pressure source to an actuator such as a pneumatic cylinder includes a fluid pressure equipment which has a switching valve for switching a flow path, a pressure control valve for controlling pressure, a filter for removing dust, water and the like from the compressed air, and a pipe arrangement for connecting the above components. Similarly, a hydraulic circuit for supplying hydraulic pressure from a hydraulic pressure source to a hydraulic actuator includes a fluid pressure equipment such as a pressure control valve. A pressure gauge for measuring pressure of fluid is used in such a fluid pressure equipment included in a fluid pressure circuit for driving an actuator which is actuated by air pressure or hydraulic pressure as described above.
There is an analog pressure gauge which displays measured pressure using an indicator needle, and a Bourdon tube type pressure gauge provided with a Bourdon tube is frequently used in this type of pressure gauge. In an analog pressure gauge provided with an indicator needle, a scale based on a measurable range of the pressure gauge is marked as a pressure scale of a scale plate indicated by the indicator needle so that the pressure gauge can be used for various fluid pressure circuits. For example, in a pressure gauge used in a pneumatic circuit, a pressure scale based on a measurable range from a minimum value of 0 Mega Pascal (MPa) to a maximum value of several MPa is marked. However, in many cases, air pressure actually supplied to a pneumatic circuit is within a range smaller than a measurable range of the pressure gauge. For example, even if up to 1.0 MPa can be measured by a pressure gauge, in a pneumatic circuit provided with the pressure gauge, fluid pressure may be used within an operating pressure range between 0.4 MPa and 0.6 MPa. In such a case, it is necessary for an operator to check whether or not air pressure supplied to each pneumatic device included in the pneumatic circuit is within a designated operating pressure range by observing the pressure gauge.
Japanese Patent No. 3717621 and Japanese Patent Application Laid-Open Publication No. 06-52215 disclose a pressure gauge provided with a preset marker indicating a pressure range.    Patent Document 1: Japanese Patent No. 3717621    Patent Document 2: Japanese Patent Application Laid-Open Publication No. 06-52215